The present invention relates to a feed carriage for holding workpieces in machine tools for machining wood or plastic, e.g. for circular saws or milling cutters.
Carriages of this type include an upper portion in the form of a light-metal profile with a clamping surface for the workpiece, a lower portion in the form of a light-metal profile which is to be fastened to the machine housing, and a center portion on which the upper portion is movably supported, as well as sets of guide rollers which are permanently connected together, the upper portion and the lower portion extending far beyond the machine housing in their longitudinal direction.
Various forms of construction of feed carriages of the above-mentioned type are known in the art. In most cases the upper and lower carriage portions have a U-shaped profile configuration, and a lip extends from the upper carriage in the direction toward the tool. In the case of machines in which the tool can be pivoted up to an angle of 45.degree. the carriage must have an oblique portion, at the side facing the tool, which extends at an angle of 45.degree. so that the lip on the upper carriage portion extends laterally far beyond the lower carriage portion.
The lower carriage portion usually has a trapezoidal design and is fastened to the machine housing via the short base of the trapezoid. Due to the overhang of the upper portion at only one lateral side thereof, the entire feed carriage is subjected to torsional stresses which result in the production of uneven edges on the workpieces as they are being machined.
Attempts have therefore been made to support the upper carriage portion at the machine housing by means of additional contact rollers. This, however, has the drawback that in such a case the lower carriage portion and the additional contact rollers must be precisely aligned with one another, since otherwise the upper carriage portion would be twisted during its movement and this would again result in inaccurately machined workpieces. A further drawback is that such additional support is possible only within the region of the machine housing.
In order to obtain a sufficiently wide clamping surface for the lower carriage portion, the upper carriage portion must of necessity be rather wide so that the operator who stands to the side of the feed carriage is required to lean over the feed carriage during its longitudinal travel.
For these reasons it has been the custom to produce two different types of feed carriage, a small and stable one for machines with a stationary tool and a wider and less stable one, which nevertheless is more complicated, for machines having a pivotal tool.